Got that backwards.
If something was undervalued why did it not immediately get bought and move to "fair value" {another bogus concept}. Some genius hasn't figured it out yet I suppose?
Price only moves when someone perceives value (a subjective concept) is higher or lower. Otherwise price is already at fair value/overvalued/undervalued/whatever.
value is subjective, a price of a good might be undervalued to some and overvalued to others and these different opinions are what make a market